Currently, gas turbine engines require a number of accessories to be driven from a core engine of the gas turbine engine. The accessories include fuel pumps, oil pumps, hydraulic pumps, electrical generators, etc. Normally, the accessories are driven by an accessory gearbox mounted on a casing of the gas turbine engine. The accessory gearbox is driven by the core engine via a radial drive shaft, which is driven by a shaft of a high-pressure rotor or an intermediate pressure rotor of the core engine.
The provision of the accessory gearbox on the casing of the gas turbine engine produces deviations to the aerodynamic flow lines of the casing around the accessory gearbox, resulting in a loss of aerodynamic flow around the casing of the gas turbine engine.
Open rotor gas turbine engines, or turbo-propeller gas turbine engines, suffer from a difficulty of providing in flight restarting of the gas turbine engine during windmilling, because there is little aerodynamic coupling between the blades of the open rotor, or blades of the propeller, and the core engine of the gas turbine engine.